1. Field of the Invention
This invention relates to screw driving bit holder devices for insert bits used to drive screws, having various drive head configurations driven manually or by power, and more particularly, to a method for depth location of the screw.
2. Description of the Prior Art
The prior art delineating holding devices for insert type bits for driving screws is substantial. The concept of, the reason for, and the description of, the insert type bit are well documented in Fischer U.S. Pat. No. 2,522,217. These items will not be re-recited here except to note they were based generally on economic considerations.
It is noted that Fischer refers to this type of bit of bit as a "unitary bit." The name "insert bit" appears in Fitch U.S. Pat. No. 2,806,706. The term "insert bit" is now used generally for this type of bit.
Numerous refinements and new utilities have been advanced for the insert bit and particularly for the bit holding devices for these bits. The most predominant of these has been the addition of permanent magnets of the Alnico type to the bit holding device. The magnetism is transfered to and through the insert bit for retention of the screw to the bit. The merits of such bit holdrers are found in F. G. Clark U.S. Pat. Nos. 2,550,775; 2,671,484; 2,677,294; 2,833,548; 3,007,504; and C. A. Lange U.S. Pat. No. 2,838,082.
The most common bit holders in use at the time of this invention, and described in the following detailed description, are of two types which are commonly known as the C-ring and the nose cap type. These are available in both magnetic and non-magnetic styles.
The C-ring type in most common use embodies the essential elements of the Fischer U.S. Pat. No. 2,522,217, including a cylindrical body with a shank for transmitting torque through the body, or alternately an integral socket recess designed to attach in a fixed relationship to a rotating power tool spindle or to a manual hand driver. Also included are a socket type recess to receive the polygonal shank of the insert bit, which now most commonly has a hexagonal shank, and a shoulder surface at the bottom of this bore to restrain the axial thrust of said bit when in engagement with a screw type fastener. Finally, there is included a spring type ring in an internal annular groove in the bore to retain the bit against axial pull out forces, either frictionally or more positively by engaging notches being supplied in almost all currently manufactured insert bits. The bit holders are prescribed and defined in federal specifications such as GGG-B-00122.
The Clark U.S. Pat. No. 2,550,775 embodies these same features as discussed above, except that the retaining ring is replaced by a permanent magnet, located in a bore at the bottom of the bit driving socket, which retains the bit magnetically, but with the added new utility of retaining the fastener magnetically on the end of the bit. Although currently in use, it is limited to applications where the relatively weak holding force of the magnet will not cause problems of a convenience or safety nature should the bit stick in the fastener recess and be pulled out of the bit holder.
The bit holder of the C-ring type in most common use at this time is a hybrid of the preceding patents, utilizing both the superior holding force of the retaining ring and the utility of the magnet as described above.
The nose cap type bit holder in most common usage at this time, either magnetic or non-magnetic, incorporates the features of the hybrid C-ring bit holder described above. These are: a cylindrical body, a shank or socket driving means, a socket recess to accept the bit, and a magnet or locating shoulder at the bottom of this recess. An exception is the retaining ring feature which is located in a separate nose cap or sleeve which has a partially threaded bore to engage like external threads on the end of the cylindrical bit holder body opposite the shank of the driven end. The retaining feature is a rubber O-ring retained in an annular groove at the bottom of the nose cap internal bore. The O-ring is compressed in the groove and against the bit by the end surface of the bit holder when the cap is threaded onto the bit holder. This compression causes very high frictional forces against the bit which resist bit pullout should the bit tend to stick in the fastener recess.
Two types of nose cap bit holders are now in common usage. One type has a threaded nose, with the major diameter of the threads being the same as, or slightly less than, the diameter of the body. The threads blend into the body, providing no distinct shoulder. The second type, having a larger body diameter, utilizes the same threads, but provides a thread relief and a distinct shoulder. This limits the O-ring compression and subsequent O-ring damage when the nose cap is threaded into place.
The nose cap of these two types of bit holders are interchangeable. This is important to the present invention. In the preferred embodiment, the nose caps are universally adaptable to both types of nose cap bit holders.
The Lange U.S. Pat. No. 2,838,082 shows a sleeve of similar construction and attachment and bit retaining means. The Lange patent differs from the most commonly used nose cap type bit holders, in that the bit driving socket means is incorporated in the unthreaded portion of the detachable sleeve. The external face of the magnet, located in a bore in the bit holder body, is essentially flush with the threaded end of the bit holder. The bit retaining means in this case is a retainer ring located in an annular groove in the socket portion of the sleeve. It is located in such a relationship with the face of the magnet as to engage the notches in the insert bit.
The most common nose cap bit holder in use at this time is then seen to be a hybrid of both the C-ring bit holder described above and the nose cap or sleeve type of the referenced Lange patent. It is also noted that the bit retaining means, used in this now most common hybrid embodiment, is a resilient continuous rubber ring, commonly referred to as an O-ring. This ring develops sufficient frictional holding force to retain the bit, independent of the notches, against normally encountered pull out forces.
An examination of the above cited patents, as well as currently developed art, indicates one commonality, that being the lack of a feature to locate the depth of the fastener relative to the work surface. It is this new utility for bit holders that the present invention addresses and provides.
Until this new utility, integral with the bit holder, was provided, the method of depth location was incorporated in the driving tools providing rotation of the bit holder shank. These were generally, but not limited to, relatively expensive electric or air driven power tools. This took the form of a depth locator adapter designed specifically for the particular power tool, and available generally only on power tools designed for screwdriving. These usually incorporated a clutching mechanism associated with the locator adapter. They were generally designed to work only with tools having the hexagonal power shanks, with the detenting annular groove, shown in several of the cited patents and standardized for industry by ANSI specification B107.4. These are the shanks of the bit holders of the two embodiments described below.
The primary purpose of this shank design was to prevent the slippage that occurs typically in three-jaw key chucks holding round shank tools, such as drills. The avoidance of such slippage is of great importance, given the higher torques and impacts associated with screw driving, and coincidentally, the prevention of axial pull out of the driven tool.
Bit holders of this type incorporating the hexagonal power shanks, as well as many other screwdriving accessories sucha as nut setters, socket adapters or extensions, power bits and bit finders, were originally designed to be used in power driven screwdrivers with compatible hex chucks. They are increasingly being used in power drills with key type three-jaw chucks because of the non-slip feature of the hex shank, and the higher torque and variable speed features now common on power drills making them better suited to screwdriving.
With the advent of battery operated screwdriving tools and drills utilizing three-jaw key chucks, and quick release chucks for the hex shank either to replace or be used in conjunction with the key chuck, ref. U.S. Pat. No. 4,692,073, the use of, and utility of, the hex shank screwdriving accessories, including the bit holders associated with the present invention, is seeing an exponential growth. It can therefore be expected that the new utility, provided by the present invention, will also experience this growth.
The following detailed description will refer frequently to bit holders having hexagon shanks. To clarify the orientation of various parts and features of these bit holders, the bit or driving end will be referred to as forward or front, and the shank or driven end will be referred to as rearward or back.